I blieve there is a limit of 6 month per year (also believe max total 2 year in 5yrs/GC expr ),
But if u need more than to any other reason, you SHOULD get a permision in advance for re-enter .
Good Luck, plz read the following
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http://uscis.gov/graphics/services/Emergency/#Reentry
Re-Entry Permit
Lawful Permanent Residents (green card holders) use re-entry permits to re-enter the U.S. after travel of one year or more. For LPR’s returning to the U.S., re-entry permits are generally valid for two years from the date of issuance of the re-entry permit. The LPR should apply for this benefit before leaving the U.S.
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Also read this.
http://uscis.gov/graphics/howdoi/PermRes.htm
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Now that you have become a Permanent Resident of the United States we would like to welcome and congratulate you on your accomplishment. Some of you came to the United States as immigrants through a relative or through an employer. Some of you came as refugees or were given asylum status. And some of you came through other programs, like the Diversity Visa Lottery. But now that you are Permanent Residents you all share the same status. You have certain rights and certain responsibilities as Permanent Residents. This document will give you a general idea of what those rights and responsibilities are and some other useful information related to your immigration status as a Permanent Resident.
Some of you may be CONDITIONAL RESIDENTS. This page applies equally to you while you are in conditional resident status. The difference between you and an unconditioned permanent resident is that your permanent resident status will expire in two years from when it was given, unless you successfully petition to have the condition removed. Those of you with conditional permanent residence either received your residence through a marriage relationship where the marriage was less than two years old at the time you became a Permanent Resident, or you received that status through an investment as an employment creation immigrant (EB-5). If you successfully petition for removal of the condition on your immigration status, this page will still apply to you as a Permanent Resident.
Rights
As a Permanent Resident you have most of the rights of a United States Citizen but there are some exceptions.
Rights
To live permanently in the United States provided you do not commit any actions that would make you removable (deportable) under the immigration law (section 237, Immigration and Nationality Act).
To be employed in the United States at any legal work of your qualification and choosing.
To be protected by all of the laws of the United States, your state of residence and local jurisdictions.
To vote in local elections where United States Citizenship is not required. Click here for more details on voting.
Exceptions
Some jobs will be limited to United States Citizens because of security concerns.
You may not vote in elections limited to United States Citizens. Click here for more details on voting.
Responsibilities
You are required to obey all of the laws of the United States, the States, and localities. You are required to file your income tax returns and report you income to the US Internal Revenue Service and State IRS. You are expected to support the democratic form of government and cannot attempt to change the government through illegal means. If you are a male, age 18 through 25, you are required to register with the Selective Service.
International Travel
A Permanent Resident of the United States can travel freely outside of the US. A passport from the country of citizenship is normally all that is needed. To reenter the US a Permanent Resident normally needs to present the green card (Permanent Resident Card, Form I-551) for readmission. A reentry permit is needed for reentry for trips greater than one year but less than two years in duration.
You can find more information about travel documents from "How Do I Get a Travel Document?"
Maintaining Permanent Residence
Maintaining Permanent Residence You may lose your permanent residence status if you commit an act that makes you removable from the United States under the law in section 237 of the Immigration and Nationality Act. If you commit such an act, you may be brought before the immigration courts to determine your right to remain a Permanent Resident.
You may be found to have abandoned your permanent resident status if you:
Move to another country intending to live there permanently.
Remain outside of the US for more than one year without obtaining a reentry permit or returning resident visa. However in determining whether your status has been abandoned any length of absence from the US may be considered, even if it is less than one year.
Remain outside of the US for more than two years after issuance of a reentry permit without obtaining a returning resident visa. However in determining whether your status has been abandoned any length of absence from the US may be considered, even if it is less than one year.
Fail to file income tax returns while living outside of the US for any period.
Declare yourself a “nonimmigrant” on your tax returns.
Naturalization
Many Permanent Residents of the United States have the ultimate goal of becoming a US citizen. Naturalization is the primary method for most persons not born as US citizens to obtain that status. Under current law naturalization is done by the federal and state courts and in an administrative proceedings. Once a permanent resident completes the necessary residence and physical presence requirements (which vary in certain cases), an application for naturalization can be filed with Immigration. This starts a review of the person’s basic eligibility, criminal and security histories, and then leads to testing of the person’s English language abilities, knowledge of the history and form of government of the US, and good moral character. Complete information on naturalization can be obtained on our Naturalization page.
As a naturalized US citizen you have the same rights and privileges as a native born US citizen with one exception. Only a native born US citizen can be president of the United States. As a US citizen you can petition for your parents and siblings to immigrate to the US. Your spouse and children (unmarried and under 21 years of age) qualify for immediate relative classification for immigration purposes, which means they do not have a waiting list to immigrate (like the spouse and children of a Permanent Resident) and can do so as fast as the paperwork can be processed.
Permanent Resident Card
The Permanent Resident Card, Form I-551, is issued to all Permanent Residents as evidence of alien registration and their permanent status in the US. The card must be in your possession at all times. This requirement means that you are not only required to have a currently valid Form I-551 at all times, but also that you must carry your currently valid Form I-551 on your person at all times. The Permanent Resident Card currently is issued with a 10-year validity. You status as a Permanent Resident does not expire with the 10-year validity. Only the card expires. The card is only valid up to the expiration date and must be renewed before it expires.
A Conditional Permanent Resident is issued a card valid for two years. In order to remain a Permanent Resident, the Conditional Permanent Resident must file a petition to remove the condition during the 90 days before the card expires. The conditional card cannot be renewed. The condition must be removed or you lose your permanent resident status. (See Form I-751 and Form I-829.
The Permanent Resident Card (either unconditioned or conditioned) can be used to prove employment eligibility in the US when completing the Form I-9 for a new employer. It can also be used to apply for a Social Security Card and a state issued driver’s license. The card is valid for readmission to the United States if the trip was not greater than one year in length. If a trip will last longer than one year, a reentry permit is needed.
Relatives
A Permanent Resident can petition for some relatives to join him or her in the United States as immigrants. Those relatives are your spouse and children, regardless of age. See our page on "Immigration through a Family Member".
If you had a spouse and children when you became a Permanent Resident, they may be eligible for permanent residence through you without filing separate petitions. This depends on how you qualified for your permanent residence. You should ask an immigration officer, attorney, or voluntary help organization for advice about this.
Voting
One of the most important privileges of democracy in the United States of America is the right to participate in choosing elected officials through voting. As a Permanent Resident you can only vote in local and state elections that do not require you to be a US citizen. It is very important that you do not vote in national, state or local elections that require a voter to be a US citizen when you are not a US citizen. There are criminal penalties for voting when you are not a US citizen and it is a requirement for voting. You can be removed (deported) from the US if you vote in elections limited to US citizens.
Change of Address
You are required to notify us of any change of address within 10 days of that change. Form AR-11 is used for that purpose. You can learn more about change of address requirements is found at "How Do I Report a Change of Address?"
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Good Luck
